1. Field of the Invention
The present invention relates to a reflection type display device constituted by semiconductor devices using thin film semiconductors, and particularly to a structure of a reflection type liquid crystal display device. Also, the present invention relates to an electronic device using the reflection type display device.
2. Description of the Related Art
In recent years, since a portable information terminal equipment (portable equipment) such as a mobile computer and a portable telephone (including PHS) has rapidly come into wide use, a reflection type liquid crystal display device attracts a great deal of attention. Since the reflection type liquid crystal display device does not require backlight as a light source, it is possible to make the portable equipment miniaturized, lightened, and decreased in consumption of electric power.
Here, a conventional process of manufacturing a pixel matrix circuit constituting a reflection type liquid crystal display device will be described in brief. The pixel matrix circuit is a circuit in which thin film transistors (TFT) for controlling an electric field applied to a liquid crystal are arranged in matrix, and constitutes an image display region of a liquid crystal display device.
In FIG. 2(A), 201 denotes a substrate having an insulating surface, 202 denotes an active layer of a first pixel TFT, and 203 denotes an active layer of a second pixel TFT. A distance between the first pixel TFT and the second pixel TFT corresponds to a pixel pitch, and has a tendency to become short as the display becomes highly minute.
Reference numeral 204 denotes a gate insulating film. Gate electrodes 205 and 206 are formed thereon. The gate electrodes 205 and 206 are connected to not-shown gate lines. In this way, the state shown in FIG. 2(A) is obtained.
Next, an impurity ion for giving one conductivity (phosphorus (P) for an N-type, and boron (B) for a p-type) is added into the active layers 202 and 203. As a result, source regions 207 and 208, drain regions 209 and 210, and channel formation regions 211 and 212 are formed (FIG. 2(B)).
Next, a first interlayer insulating film 213 is formed, contact holes are made, and source electrodes 214 and 215 and drain electrodes 216 and 217 are formed. In this way, the state shown in FIG. 2(C) is obtained.
Further, a second interlayer insulating film 218 is formed, and a black mask 219 is formed thereon. A third interlayer insulating film 220 is formed thereon, and finally pixel electrodes 221 are formed. The respective pixel electrodes 221 are made of a metal thin film which reflects incident light, so that the pixel electrodes are made to have a function as a reflecting electrode (FIG. 2(D)).
At this time, the black mask 219 is disposed under a region which is a gap between the pixel electrodes (reflecting electrodes) 221. In FIG. 2(D), although the black mask appears to be individual patterns, all the patterns are actually connected in matrix. The black mask 219 arranged in this manner serves to block light leaked from the gap of the pixel electrodes 221.
Through the above steps, the pixel matrix circuit as shown in FIG. 2(D) is completed. Then, by a well-known cell assembling step, a liquid crystal is held between the substrate on which the pixel matrix circuit is formed and an opposite substrate, so that a reflection type liquid crystal display device is completed.
As an example different from the structure shown in FIG. 2(D), it is also possible to use the source electrodes 214 and 215 as black masks by adjusting the source electrodes 214 and 215 to the gaps between the pixel electrodes 221. However, the line width of the source/drain electrodes has a tendency to be made minute, and further, in view of the patterning precision (affecting the distance of the gap) of the pixel electrode, it may be said that there is a limit to this proposal.